The present disclosure relates to coating compositions, and more particularly, to coating compositions that form films exhibiting anti-fog and/or anti-condensation properties.
There are numerous instances in which optically clear articles would be enhanced if they were resistant to the formation of a fog on a surface of the article, for example, in window applications such as for greenhouses.
In general, fog and condensation formation occur under conditions of high humidity and high temperature or at interfacial boundaries where there is a large temperature and humidity difference. Coatings that reduce the tendency for surfaces to xe2x80x9cfog upxe2x80x9d have been reported. These so-called anti-fog coatings improve the wettability of a surface by allowing a thin layer of water film to form on the surface instead of discrete droplets. Known anti-fog coatings include, for example, coatings using ammonium soap, such as mixtures of an alkyl ammonium carboxylates with a surface active agent, for example, a sulfated or sulfonated fatty material; salts of sulfated alkyl aryloxypolyalkoxy alcohol; or alkylbenzene sulfonates. Other common anti-fog coating compositions use colloidal silica to provide water resistance. However, colloidal silica coating compositions generally have a high solvent content and are generally less effective for controlling condensation. Other common anti-fog compositions require chemical crosslinking to form a cohesive film. Although less solvent is used, the chemical crosslinking can significantly affect film properties. A highly crosslinked coating can cause the coated film to be brittle whereas low crosslinking can result in chalking, i.e., a powdery film that degrades or disperses upon contact with an aqueous solution.
Although the above noted coating formulations have addressed some of the problems in the field, none provides a total solution. Most of the formulations have low moisture absorptivity, long moisture release time, and/or poor water and solvent resistance. For example, water-soluble silicone resins synthesized from hydrophilic functional group-bearing silane compounds generally have poor water resistance, inadequate film hardness and poor weathering resistance. Some of these formulations also have inefficient fabrication processes, e.g. a long coat curing time. To be useful in most commercial applications, the anti-fog coating should possess high clarity, possess a long shelf life prior to coating, exhibit impact resistance properties suitable for the intended application, be able to absorb and release moisture simultaneously, and be able to resist water and conventional organic solvents, such as alcohols, alkylbenzenes (e.g., toluene), glycol ethers (e.g., propylene glycol monomethyl ether), and alkyl ketones (e.g., methyl ethyl ketone).
Disclosed herein is an anti-fog coating composition comprising a silicone compound, a water dispersible polyurethane compound, and water.
A process for forming an anti-fog film on a substrate comprises applying an aqueous coating composition to the substrate, wherein the aqueous coating composition comprises a silicone compound, a water dispersible polyurethane compound, and water; and coalescing the silicone compound and polyurethane compound to form a film.
In another embodiment, a process for forming an anti-fog film comprises applying a coating composition to a substrate, wherein the coating composition comprises a silicone compound, an isocyanate, a polyol and a catalyst; and crosslinking the coating composition to form a film, wherein crosslinking comprises heating the substrate to a temperature and for a time effective to form the film.
A glass or plastic article having an anti-fogging surface comprises a glass or plastic substrate and an anti-fog coating disposed on at least one surface of the substrate, the anti-fog coating comprising a silicone compound, a water dispersible polyurethane compound, and water.
In another embodiment, glass or plastic article having an anti-fogging surface comprises a glass or plastic substrate; and an anti-fog coating disposed on at least one surface of the substrate, the anti-fog coating comprising a crosslinked film formed from a silicone, an isocyanate, a polyol and a catalyst.
These and other features will be apparent from the following detailed description.